The present invention relates to a structure of a carbon fiber molded acoustic diaphragm having high strength.
Carbon fiber is widely used in fabricating sporting goods and military supplies because of its high strength, low weight and excellence in flexibility. For example, carbon fibers are added into aluminum alloy to produce a golf shaft or into plastic materials to form a carbon fiber reinforced plastic (CFRP) for producing tires. In recent years, carbon fibers are also employed as acoustic diaphragms of planar diaphragm speakers. The acoustic diaphragm of a typical planar diaphragm speaker is relatively stiff and substantially flat and supported by a frame. The acoustic diaphragm is vibrated by an electromagnetic driver coupled to the rear surface thereof so as to emit sound. Generally, the acoustic diaphragm is conducted by combining at least two carbon fiber layers.
FIGS. 1 and 2 show two types of acoustic diaphragm according to prior art. Referring to FIG. 1, the acoustic diaphragm 10 is formed by coupling two carbon fiber layers 11 and 12. The fibers 110 of the upper carbon fiber layer 11 and the fibers 120 of the lower carbon fiber layer 12 are perpendicular to each other. Since the applied stresses on the both layers 11 and 12 are usually not uniform, the ends will be raised and therefore could not be used in a planar diaphragm speaker. Referring to FIG. 2, an acoustic diaphragm 20 is formed by coupling three carbon fiber layers 21, 22 and 23 from top to bottom. The fibers 210 of the top layer 21 and the fibers 230 of the bottom layer 23 are parallel with each other but perpendicular to the fibers 220 of the medium layer 22. It is known in the art that the thickness of each layer is about 0.1 mm. The three carbon fiber layers 21, 22 and 23 are then subjected to a heating and pressing process to form the composite layer 20 to be used as an acoustic diaphragm. It is found that the structure of the carbon fiber composite layer 20 could only slightly increase the strength thereof; however, the three layers"" structure brings about increase in weight.
Therefore, the present invention provides an improved structure of an acoustic diaphragm for overcoming the problems described above.
It is an object of the present invention to provide a method for forming a composite carbon fiber layers, wherein the composite carbon fiber layer could be used as an acoustic diaphragm adapted to be used in a planar diaphragm speaker.
It is another object of the present invention to provide a structure of an acoustic diaphragm, which is a composite carbon fiber layer of two carbon fiber layers.
It is another object of the present invention to provide a structure of an acoustic diaphragm having high strength.
In accordance with an aspect of the present invention, there is provided a method for forming a composite carbon fiber layer. The method includes steps of providing two carbon fibers layers having fibers in parallel with each other and disposed in a stacked form, and heating and pressing the two carbon layers simultaneously to form the carbon fiber composite layer.
Preferably, the heating and pressing step is carried out at about 130xc2x0 C. under 300 psia for 60 minutes.
Preferably, the carbon fiber composite layer further includes a first vibration absorber layer between the top carbon fiber layer and the bottom carbon fiber layer. In addition, the carbon fiber composite layer further includes a second vibration absorber layer disposed on the top carbon fiber layer and a third vibration absorber layer disposed under the bottom carbon fiber layer.
Preferably, each of the first vibration absorber layer, the second vibration absorber layer and the third vibration absorber layer is made of high-density polyethylene (HDPE).
Preferably, the thickness of the top carbon fiber layer is about 0.1 mm and the thickness of the bottom carbon fiber layer is about 0.1 mm.
In accordance with another aspect the present invention, there is provided a structure of an acoustic diaphragm, which includes a bottom carbon fiber layer and a top carbon fiber layer disposed on the bottom carbon fiber layer, wherein the fibers of the top carbon fiber layer and the fibers of the bottom carbon fiber layer are parallel with each other.
Preferably, the acoustic diaphragm further includes a first vibration absorber layer between the top carbon fiber layer and the bottom carbon fiber layer. In addition, the acoustic diaphragm further includes a second vibration absorber layer disposed on the top carbon fiber layer and a third vibration absorber layer disposed under the bottom carbon fiber layer.
Preferably, each of the first vibration absorber layer, the second vibration absorber layer and the third vibration absorber layer is made of high-density. polyethylene (HDPE).
Preferably, the thickness of the top carbon fiber layer is about 0.1 mm and the thickness of the bottom carbon fiber layer is about 0.1 mm.
In accordance with another aspect of the present invention, there is provided a structure of an acoustic diaphragm adapted to be used in a planar diaphragm speaker. The structure includes a bottom carbon fiber layer having a first fiber direction, a first vibration absorber layer disposed on the bottom carbon fiber layer, and a top carbon fiber layer disposed on the bottom carbon fiber layer and has a second fiber direction, wherein the first fiber direction and the second fiber direction are parallel with each other.
The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: